Monitors a file or directory for changes.
To obtain a FileMonitor for a file or directory, use monitor, monitor_file, or monitor_directory.
To get informed about changes to the file or directory you are monitoring, connect to the changed signal. The signal will be emitted in the thread-default main context of the thread that the monitor was created in (though if the global default main context is blocked, this may cause notifications to be blocked even if the thread-default context is still running).